Biomedical subjects
Publications and source records attributed to R W Winters.
The spatial distribution of the surround's adaptive sensitivity was assessed in the receptive fields of cat retinal ganglion cells. The results provide evidence that the surrounds adaptive sensitivity is higher in the center of the receptive field of Y-cells than X-cells.
The spatial distribution of the surround's adaptation mechanism was studied in X- and Y-cells in the cat's retina. Adaptive sensitivity was assessed with adapting annuli with equal-area, but variable position and with adapting annuli with variable size. The results provide evidence that adaptive sensitivity of the surround's adaptive mechanism is higher in the center of the receptive field of Y-cells than of X-cells.
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A comparison was made between adaptive and signal sensitivity profiles of the surround response mechanism of cat retinal ganglion cells. The 2 profiles were found to be similar for X cells but the surrounds of Y cells appear to pool adaptation over a smaller retinal region than they pool signals.
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The summing properties of the surround response mechanism of cat retinal ganglion cells were assessed by determining area-sensitivty and area-adaptation curves. The two curves were found to be similar for X and Y cells but for many Y cells adaptive sensitivity was found to be dependent upon the size of the test target. These results suggest that, for X cells, the retinal area over which the surround integrates signals and adaptation are spatially coextensive. Most Y cells appear to pool adaptive effects over a smaller region than they pool signals.
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Single optic tract fibers in the cat were classified as X or Y cells by a contrast reversal stimulus. A slit of light was then moved across the receptive field at velocities from 10--1000 degrees/s. The preferred velocity was that velocity which elicited the strongest response from the cell. The maximum velocity was the highest velocity target to which a cell could respond. Y cells as a group both preferred and could follow faster targets than X cells, and were more broadly tuned to the preferrred velocity.
The adaptation field of the surround mechanism of X and Y retinal ganglion cells in the cat was assessed with variable size, unmodulated adapting spots. Both an on-inhibition measure and an off-discharge measure of surround gain was used. Results suggest that the surround mechanism in Y-cells is strongest in the receptive field middle but weak or nonexistent in the middle of X-cell receptive fields.
The surround response mechanism in on-center X-cells in cat retina was found to be bimodally distributed and weak or nonexistent in the receptive field middle. An on-inhibition measure was used to assess surround mechanism gain.
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Maintained firing rates of X cells and Y cells were compared at 6 adaptation levels (AL) between -2.71 log cd/m2 and 2.28 log cd/m2 (10 mm2 pupil size). X cell maintained firing was higher at all ALs and was statistically different at medium and high ones. Changes in AL had nearly identical effects upon X and Y cell suprathreshold sensitivity to a flashing spot in the center of their receptive fields; the Weber function had a slope of 0.744 for Y cells and 0.743 for X cells. These values are not statistically different.
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Explore the source record for details and available documents.